B Cells in Health and Disease – Leveraging Flow Cytometry to Evaluate Disease Phenotype and the Impact of Treatment with Immunomodulatory Therapeutics

Flow Cytometers are key devices used to monitor the composition of cells in the blood in the setting of a variety of disease states. Recent advances have produced a range of instruments that range from simple desktop-type devices to multi-laser platforms that allow for high complexity measurements. This variety of instrumentation makes the technology suitable for different budgets, expertise levels and intended uses (research versus diagnostic) with a set of reagents that can effectively be used on any platform so long as the laser line can excite the given fluorochrome and the optics are set up to discriminate emission from the excitation wavelength. Traditional medical applications for flow cytometers include evaluation of CD4 T cell depletion and associated immunophenotypic changes in HIV-infected persons as well as characterization of aberrant cell types used to diagnose hematologic malignancies. More recently, investigators have not only extended immunophenotyping campaigns to other disease settings, but have also taken advantage of fluorescent probes that provide insight into cellular function. For example, it can be inferred that a cell that expresses CD107 on its surface has likely participated in the delivery of cytotoxic granules to a target cell (Michael R.Betts, 2004). Likewise, amine-reactive dyes can be used to track cell division, probes that fluoresce only after enzymatic cleavage can report on caspase activities in apoptosis experiments and intracellular phosphorylation can be measured with specific antibodies and cell permeabilization buffers (phosphoflow) (Maxwell et al., 2009; Krutzik and Nolan, 2006; Wu et al., 2010). The elegance of the flow cytometry platform relies on its simplicity in as much as any combination of fluorescently-conjugated probes can be used to address contemporary hypotheses in cell biology and immunology. It is therefore not surprising that investigators have introduced flow cytometric measurements in biomarker campaigns to study a variety of activities of an immunomodulatory therapeutics), including effects of proximal signaling events as influenced by agonist or antagonistic drugs, or cell immunophenotype as a representative distal pharmacodynamic marker in treated persons.